Method and apparatus for multimedia communication

ABSTRACT

A method and apparatus for enabling communication of IP multimedia content to a called user during a circuit-switched call between a calling terminal (A) having called a primary communication unit (B 1 ), when the call has been forwarded to a secondary communication unit (B 2 ). The calling terminal receives a connected number during a call set-up procedure, e.g. by subscribing to a called line presentation (COLP) service. The calling terminal stores the received connected number and determines multimedia capabilities of the secondary communication unit based on the connected number. Available multimedia options can then be determined based on the multimedia capabilities of the secondary communication unit.

TECHNICAL FIELD

The present invention relates generally to a method and apparatus forcommunicating multimedia over an IP communication network during acircuit-switched call. In particular, the invention enables multimediacommunication when a called terminal is subject to call-forwarding toanother communication unit.

BACKGROUND OF THE INVENTION AND PRIOR ART

Until recently, wireless mobile terminals have been used basically formaking voice calls. Standardised and well-established communicationtechnologies and protocols are then utilised to communicate voicebetween fixed and/or mobile terminals using circuit-switchedcommunication channels.

However, a multitude of new telephony services involving “multimedia”are now rapidly being developed, enabled by the introduction of newtechnologies allowing for notably higher transmission rates andincreased network capacity. For example, GPRS (General Packet RadioService) and WCDMA (Wideband Code Division Multiple Access) technologiesare currently emerging for enabling wireless telephony servicesrequiring a wide range of transmission rates and different protocols andmedia formats.

The trend today is also a move towards packet-switched networks andtechnologies providing more capacity and flexibility as compared to thetraditional circuit-switched networks. Further, new sophisticated mobileterminals are also emerging on the market, equipped with functionalityto handle the new services, including high resolution colour displaysand various codecs (coders/decoders) e.g. for visual information.

Multimedia services typically involve transmission of data representingtext, documents, images, audio files and video files in a multitude offormats and combinations, and according to various different protocols.The term “multimedia” will be used in this description as generallyreferring to telephony services involving the transfer of any choice ofmedia, typically with visual content, apart from ordinary voice, over apacket-switched network.

A prevailing goal or ambition in the field of telecommunication is toconverge all services on to a single transport mechanism—the packetbased Internet Protocol (IP), regardless of the type of access networksand technologies involved. A network architecture called “IP MultimediaSubsystem” (IMS) has therefore been developed by the 3^(rd) GenerationPartnership Project (3GPP) as an open standard, to give operators ofaccess networks the ability to offer multimedia services in the packetdomain. IMS is a platform for enabling services based on IP transport,involving the communication of multimedia content from one terminal toanother over an IP network. IMS is more or less independent of theaccess technology used, and is basically not restricted to any limitedset of specific services.

When using multimedia services, the prerequisites for a specific sessionwill vary depending on the invoked service and the capabilities of thecalling and called terminals, respectively, as well as on other factors.During a session, certain session parameters defining the rules ofcommunication must be used by both the calling and called terminals inorder to communicate the desired information. Such session parametersare related to codecs and storage means available in each terminal, aswell as applications and signalling protocols.

Since many different types of terminals are available on the consumermarket, two terminals about to communicate multimedia will most likelyhave different capabilities in some respect, and each terminal hastypically no knowledge of the capabilities of the other. In order toestablish an IP multimedia session, session parameters must thereforefirst be selected and established in a session set-up procedure, whichis a kind of negotiation between the two terminals.

Thus, the terminals must exchange information regarding their specificcapabilities and preferences, in order to agree on which sessionparameters to use during a forthcoming IP multimedia session, hereafterreferred to as “capability exchange” for short. A specification forsession set-up has been defined called “SIP” (Session InitiationProtocol, according to the standard IETF RFC 3261 et al). SIP is anapplication-layer control (signalling) protocol for creating, modifyingand terminating sessions over a packet-switched network. The SIPstandard is used by the above-mentioned IMS system to establish andcontrol IP multimedia communications.

In the SIP protocol, a method called “INVITE” is defined when terminalsabout to communicate multimedia basically exchange their capabilitiesduring the multimedia session set-up procedure. In this method, acalling terminal sends a session invitation message called “SIP INVITE”to a called terminal including its own capabilities, which then respondsby sending over its capabilities to the calling terminal. In this way,both terminals will become aware of each other's capabilities, and candetermine accordingly which applications and codecs that can be used inthe forthcoming session.

Another method called “OPTIONS” is also specified in the SIP protocolallowing a terminal to query another terminal as to its capabilitiesregarding codecs and supported applications, without the user actually“calling” the other party. However, the user must of course first enterthe telephone number of the other terminal. According to this method,the terminal then sends a capability query called “SIP OPTIONS” to theother terminal, preferably including its own capabilities, whichresponds by sending over its capabilities to the querying terminal. A“SIP OPTIONS update” message can also be sent if the capabilities arechanged at a later stage.

The OPTIONS method can also be used during an ongoing voice call forenriching the call with multimedia communication. By way of example, auser may wish to send an image, a document, a video clip or audio clip,to the other user during an ongoing voice call, in order to discuss itat the same time. After exchanging their capabilities, the terminals mayfurther indicate the optional multimedia available to its users, e.g. bydisplaying available services and/or applications as icons or the likeon a terminal screen. A user can then easily select which type ofservice and media to use in a forthcoming session with the other party.

When the user presses a key or the equivalent on his/her terminal forsubmitting some selected content, the terminal first sends a sessioninvitation message, inviting the other terminal to execute an IPmultimedia session involving the transfer of the selected content,before submitting the actual content. The session invitation contains adescription of the selected content/media, typically includinginformation on the activated application as well as the coded format(e.g. jpeg, gif or 3gp) and data size (e.g. 50 Kbytes) of the selectedcontent, thereby indicating what codec, application and storage capacityare required to receive the content. If the SIP standard is used in thisprocedure, the session invitation is the above-mentioned SIP INVITEmessage. Thus, the session invitation effectively queries the terminalif it is capable of receiving the selected content.

In PCT/SE03/01901, a solution is disclosed where the capability exchangeprocedure can be bypassed by storing (or “caching”) in each terminal thecapabilities of the other terminal after a first multimedia session.When a second session is to be conducted between the same two terminalsat a later occasion, the stored capabilities can be retrieved and used,merely by recognising the opposite terminal, in order to save time andsignalling.

Hence, the terminal of a calling user can normally use any of theabove-described methods to determine the capabilities of the terminal ofa called user, in order to execute a multimedia session between the twoterminals. However, the called user may have activated a call-forwardingservice, meaning that any calls directed to a called primarycommunication unit are routed to a secondary communication unit instead,as selected by the called user. The re-routing of circuit-switched callsupon call-forwarding is generally handled by a service node or “core” inthe home network of the called unit, which is a well-known procedure andtherefore not necessary to described here further.

In different implementations of the call-forwarding service, thesecondary communication unit may be a voice mail apparatus in which aspoken message or the like from the first user can be recorded andstored for later retrieval, or another terminal at which the calleduser, or another appointed person, can be reached. Calls may beforwarded in this way e.g. upon busy, no reply or immediate condition.Moreover, a call filtering function may be used where some specificcallers will be forwarded and others will not. For example, all internalcalls to a terminal within a private enterprise network may be directlyconnected, whereas all external calls to that terminal may be forwardedto a secretary's telephone or a voice mail apparatus.

A user calling another user by dialling the telephone number of aprimary communication unit may wish to convey some multimedia contentduring the call to the called user, such as an image or a video or audioclip, even if the call has been forwarded to a secondary communicationunit, such as another terminal or a voice mail apparatus.

However, it is currently not possible to send multimedia content to thesecondary communication unit after calling the number of the primarycommunication unit, since there is no mechanism available to execute theabove-described necessary capability exchange with a forwarded-tosecondary communication unit. Any messages in current capabilityexchange procedures for multimedia, such as the above-mentioned SIPOPTIONS and SIP INVITE messages, are exclusively directed to the calledtelephone number, i.e. the number of the primary communication unit.Therefore, no capabilities can be exchanged with the secondarycommunication unit. The calling terminal (and its user) may not even beaware that the call has been forwarded.

Thus, when a call-forwarding service has been activated, the desiredcontent cannot be conveyed to the secondary communication unit unlessthe calling user can make a new call directly thereto. This is a seriousdrawback, not least because the calling user is normally not aware ofthe fact that the call has been forwarded to another terminal than theone called. Moreover, it is typically not possible to call a voice mailapparatus directly.

These shortcomings will of course be perceived as a problem by terminalusers not being able to convey IP multimedia content subject tocall-forwarding, as well as by the network operators concerned beingdeprived of potential revenue from multimedia traffic. Hence, it isdesirable to overcome the problem of conveying multimedia content duringan ongoing call to a user currently utilising a call-forwarding service.It is also desirable to determine which multimedia options are availablein communication with a terminal or voice mail apparatus to which callsare forwarded.

SUMMARY OF THE INVENTION

It is an object of the present invention to enable communication of IPmultimedia content to a called user from a calling terminal when thecall is subject to call-forwarding. It is another object of the presentinvention to provide a solution for determining the capabilities of thesecondary communication unit, to enable indication of availablemultimedia options at the calling terminal, e.g. by displaying availableservices and/or applications as icons or the like on screen.

These objects and others are obtained by providing a method of enablingcommunication of IP multimedia content to a called user from a callingterminal having called a primary communication unit, when the call hasbeen forwarded to a secondary communication unit and a connected numberis received during a call set-up procedure. The calling terminal storesthe received connected number and determines multimedia capabilities ofthe secondary communication unit based on the connected number.Available multimedia options can then be determined based on thedetermined multimedia capabilities of the secondary communication unit.

The connected number may be received as the calling terminal subscribesto a connected line presentation (COLP) service. The secondarycommunication unit may be a communication terminal or a voice mailapparatus.

The multimedia capabilities of the secondary communication unit may bedetermined by requesting capabilities from the secondary unit based onthe stored connected number. Capabilities are then preferably requestedfrom the secondary unit by sending a capability query (e.g. SIP OPTIONS)or a session invitation (e.g. SIP INVITE), using the stored connectednumber as the destination address.

Alternatively, the multimedia capabilities of the secondarycommunication unit may be determined by retrieving cached capabilitiesof the secondary unit based on the stored connected number. The cachedcapabilities are then preferably retrieved by using the connected numberas a key.

The present invention also refers to a communication terminal capable ofmultimedia communication and of receiving a connected number during acall set-up procedure when calling a primary communication unit and thecall has been forwarded to a secondary communication unit. The terminalincludes means for storing the received connected number and means fordetermining multimedia capabilities of the secondary communication unitbased on the connected number. The terminal is preferably adapted todetermine available multimedia options based on the determinedmultimedia capabilities of the secondary communication unit.

The terminal may be adapted to receive the connected number by means ofsubscription to a connected line presentation (COLP) service.

The terminal may be adapted to determine the multimedia capabilities ofthe secondary communication unit by requesting capabilities from thesecondary unit based on the stored connected number. In that case, theterminal may be further adapted to request capabilities from thesecondary unit by sending a capability query (e.g. SIP OPTIONS) or asession invitation (e.g. SIP INVITE), using the stored connected numberas the destination address.

The terminal may also be adapted to alternatively determine themultimedia capabilities of the secondary communication unit byretrieving cached capabilities of the secondary unit based on the storedconnected number. The terminal may then be further adapted to retrievethe cached capabilities by using the connected number as a key.

Further features and benefits of the present invention will be apparentfrom the detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by means ofpreferred embodiments and with reference to the accompanying drawings,in which:

FIG. 1 is a schematic view of a communication scenario where the presentinvention may be used.

FIG. 2 is a flow chart illustrating a basic procedure for determiningcapabilities, in accordance with one embodiment.

FIG. 3 is a signalling diagram illustrating an exemplary procedure forexchanging capabilities, in accordance with the present invention.

FIG. 4 is a flow chart illustrating an exemplary procedure fordetermining available multimedia options, in accordance with anotherembodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates schematically an exemplary basic communicationscenario where the present solution may be used, when a communicationterminal A directs a circuit-switched call to another communicationterminal B1 being subject to call-forwarding. In this case, terminal Ais a mobile terminal currently in radio connection with a first accessnetwork 100.

Thus, the user of terminal B1 has activated a call-forwarding service todirect incoming calls to another communication terminal B2 differentfrom terminal B1, whenever a predefined call-forwarding condition isfulfilled. The shown terminals A, B1 and B2 may be any types ofcommunication units and the present invention is not limited in thisrespect. In the following description, the originally called terminal B1will be generally referred to as the “primary communication unit” andthe forwarded-to terminal B2 will be generally referred to as the“secondary communication unit”.

The called primary unit B1 is registered with a second “home” network102 comprising a service core adapted to handle circuit-switched (CS)communication and services, schematically illustrated as CS core 102 c.In particular, CS core 102 c will forward any calls aimed at primaryunit B1 to the secondary unit B2. In this context, it is of nosignificance whether the called primary unit B1 is currently inconnection with any access network or not. Alternatively, the secondaryunit to which incoming calls are forwarded may be a voice mail apparatusB2′ in the home network 102 of primary unit B1. Recording and storingvoice mail messages is a basic network service particularly for mobileterminal subscriptions. In this example however, the secondary unit B2is illustrated as a fixed telephone connected to a third access network104.

The networks 100, 102 and 104 are typically interconnected by means of ageneric “backbone” network 106, which in practice may be any type ofcommunication network, or combination of different networks. It isassumed that terminals A, B1, B2 and networks 100-106 are capable ofusing any required well-established communication techniques, and theseare not necessary to describe further to understand the presentinvention. At least access networks 100 and 104 further include servicecores adapted to handle packet-switched (PS) multimedia sessions andservices, e.g. according to the above-described IMS system,schematically illustrated in the figure as PS cores 100C and 104C,respectively. Access networks 100 and 104 also include corresponding CScores 100 c and 104 c, respectively.

By way of example, typical call-forwarding conditions may be thatincoming calls are forwarded if primary unit B1 is busy in another call,or that the call is for some reason not answered within a predefinedtime-out period. The primary unit B1 may not be connected to any accessnetwork, e.g. not powered-on or out of radio coverage in the case of amobile terminal. Another type of call-forwarding condition is animmediate condition, such that incoming calls are forwarded immediatelyregardless of the current availability or status of primary unit B1.Further, various call filtering functions may also be applied dependenton the identity of the calling party. However, the present invention andthe embodiments described below are not limited to any specificcall-forwarding conditions.

After a circuit-switched call has been established between terminal Aand secondary unit B2, the calling user at A may wish to communicatemultimedia content with the other user at B2 during the ongoing voicecall, e.g. by sending an image, a document, a video clip or audio clip.Alternatively, the calling user may simply wish to investigate whichmultimedia options are available with respect to the capabilities of theother user's terminal, before deciding to send anything. It is likelythat the terminals A and B2 have different capabilities with respect tocodecs, applications and/or memory storage size, and their capabilitiesmust therefore be exchanged first to determine these factors, asdiscussed above.

As mentioned above, there is currently no mechanism for performing therequired capability exchange with a communication unit being subject tocall-forwarding since existing conventional routines are based on acalled number, i.e. the number of B1 and not B2 in this case. However,the present invention provides a solution to this problem. FIG. 2 is aflow chart illustrating a basic procedure, according to one embodiment,of how a calling terminal can determine capabilities of a communicationunit to which a call has been forwarded. FIG. 2 will now be describedwith further reference to the scenario in FIG. 1.

In a first step 200, a user of terminal A has entered the telephonenumber of primary unit B1, and a call is directed thereto in a callset-up procedure. In order to enable multimedia communication during thecall, terminal A must then determine the capabilities of the oppositecommunication unit. Many existing networks of today provide a service ofdisplaying a connected number on a terminal screen to the user,typically referred to as “Connected Line Presentation, COLP”, by sendingthe connected number to the calling terminal. If no such service isprovided, this number can be obtained anyhow, which will be described inmore detail later below.

In the basic procedure of FIG. 2, it is determined in a next step 202whether terminal A has received a connected number during the callset-up. If not, the calling terminal A will attempt to determine thecapabilities of the opposite unit based on the called number in afollowing step 204, e.g. by means of a conventional capability query orexchange. The determined capabilities can then be used for multimediacommunication if the call has not been forwarded. Otherwise, terminal Awill try to determine the capabilities of the “wrong” unit, i.e. unitB1, instead of the forwarded-to unit B2, in step 204.

However, if it is determined in step 202 that a connected number hasbeen received, terminal A determines the capabilities based on theconnected number instead of the originally called number, in a followingstep 206. If the received connected number is different from the callednumber, the call has probably been forwarded to another terminal orunit, in this case to secondary unit B2, by means of a conventionalcall-forwarding procedure. In that case, terminal A effectivelydetermines the capabilities of the secondary unit B2 in step 206. On theother hand, if the connected number is the same as the called number,the call has not been forwarded and terminal A consequently determinesthe capabilities of primary unit B1 in step 206. Hence, by using theconnected number when available, it is not necessary for the callingterminal A to “know” whether the call has actually been forwarded ornot. Capabilities will be determined for the correct unit in step 206 ineither case.

In different alternatives at step 206 or step 204, capabilities can beobtained by request in connection with either a multimedia sessionset-up (e.g. by sending a SIP INVITE) or a capability query (e.g. bysending a SIP OPTIONS), according to conventional procedures. Thus, thepresent invention is not limited in this respect. It should be notedthat any capability queries or requests are transferred over apacket-switched part of the networks and would therefore not besubjected to the CS implemented call-forwarding service, if activated,when addressed to the primary unit B1. Any capability request musttherefore be addressed directly to the secondary unit B2.

With reference to a signalling diagram in FIG. 3, a more detailedexemplary procedure will now be described for determining capabilitiesof a communication unit when subject to call-forwarding, again withfurther reference to FIG. 1. The procedure starts with the user ofterminal A entering the number of primary unit B1 in order to make anordinary circuit-switched voice call to the user of B1. In responsethereto, a conventional call set-up request is first sent from terminalA to the CS core 100 c of the access network 100 to which terminal A isconnected, in a first step 300.

In a next step 302, the set-up request is conveyed to the CS core 102 cin the home network 102 to which primary unit B1 belongs, based on thecalled number. If the service of displaying the connected number isused, e.g. COLP, a request for the connected number is indicated in theset-up request sent in step 302, typically as a COLP indication.

In response to the set-up request, the receiving CS core 102 c may thensend a conventional call set-up message in a step 304 towards the calledprimary unit B1. If unit B1 is a mobile terminal, this would typicallyinvolve a conventional paging routine in order to locate the terminal.The next step 306 schematically illustrates that the called unit B1 doesnot respond, e.g. due to being busy, not connected, or simply notanswered. Alternatively, CS core 102 c may detect that the call is to beforwarded as an immediate condition when checking the incoming number ofB1, and then steps 304 and 306 would not be executed. Thus, theexecution of steps 304 and 306 will depend on the forwarding conditiondefined for B1, which however is not significant for the presentinvention.

Generally speaking, CS core 102 c has now somehow detected that the callis to be forwarded to secondary unit B2, when receiving the set-uprequest in step 302. Therefore, as a response thereto in a next step308, the CS core 102 c sends a new set-up request to the CS core 104 c,which is similar to the one received in step 302 although based on thereceived number of the secondary unit B2. In the case if unit B2 is amobile terminal, the set-up request would again be sent to acorresponding CS core in the home network of the mobile terminal, andthe terminal would be located using a paging routine. In this example,however, unit B2 is illustrated as a fixed telephone.

The set-up request of step 308 includes the connected number request ifreceived from CS core 100 c in the previous set-up request of step 302.In a possible development of the present solution, CS core 102 c may adda connected number request to the set-up request of step 308, if notreceived from CS core 100 c, or the CS core 104 c in network 104 of B2may later provide the connected number automatically, without requiringa specific request. However, a COLP subscription is typically requiredin existing systems to convey the connected number to the callingterminal. As evident from steps 202 and 206 in FIG. 2 above, it isimportant for the present solution that the number of the secondary unitB2 is somehow obtained at the calling terminal A such that anycapability request or query can be addressed correctly.

Similar to step 304, CS core 104 c now sends a conventional call set-upmessage in a step 310 towards the called secondary unit B2. This time,the call is answered and unit B2 responds by sending a conventionalconnect message in a next step 312 to its CS core 104, which in turngenerates a connect message towards A's CS core 100 c in a step 314,including the connected number. Finally, a connect message is sent tothe calling terminal A in a step 316.

Significantly, the connected number, i.e. the number of the secondaryunit B2, is now included in the connect messages of steps 314 and 316,e.g. according to the COLP service. The connected number of B2 has nowreached the calling terminal A and may then be displayed on its screen,in accordance with this service. The connected number is typically aso-called E.164 number as defined according to the standard 3GPP TS24.008 which is generally valid for both fixed and mobile terminals. Inthe case when the forwarded-to communication unit is a voice mailapparatus, e.g. B2′, the connected number may be defined as the E.164number of the called primary unit B1 plus an added prefix, e.g.888-0709123456 if the called number is 0709123456.

In preparation of determining the capabilities of unit B2, the callingterminal A now stores the received connected number of unit B2 for laterretrieval, in a step 318. An ordinary voice call between A and B2 hasnow been established by means of call-forwarding, and is conducted asillustrated by a next step 320.

During the voice call, the user of terminal A decides to send somemultimedia content to the user (or apparatus) having answered at thesecondary unit B2, e.g. an image, a document, a video clip or audioclip. In this example, the user first wants to check which multimediaoptions are available before sending the content. Alternatively, theuser may directly activate a suitable multimedia application in his/herterminal A and select the content from a storage means in the terminalto be conveyed to unit B2. As described above, terminal A must firstdetermine capabilities of the connected unit B2 before any multimediacontent can be communicated. In some implementations, a terminal mayautomatically determine capabilities of the opposite unit, not triggeredby any user input, in preparation for multimedia communication.

As described above, determining available multimedia options typicallyincludes sending a capability query, e.g. a SIP OPTIONS message, to thecalled party, which is packet-switched over the PS core 100C in theaccess network 100 of the calling terminal A and the corresponding PScore 104C in the access network 104 of the called unit B2. If IMStechnology is used for multimedia communication in networks 100 and 104,the PS cores 100C and 104C are typically referred to as “IMS cores”.

However, since any capability queries or requests are conventionallydirected to the originally called number, another procedure is requiredwhen call-forwarding is used. The present solution prescribes that thecalling terminal A uses the number obtained in step 316 and stored instep 318 as the connected number, in this case the number of theforwarded-to unit B2, as the destination for sending the capabilityquery to the PS core 100C, in a next step 322. If the call has otherwisenot been forwarded, the received connected number would be that of thecalled unit B1.

PS core 100C must now translate the received number into a valid IPaddress in order to have it routed by packet-switching to the targetunit B2, as indicated in a step 324, since the received connected numberis only valid in the CS part of the networks. This number translationcan be made using conventional procedures. In particular, in the IMScontext and if the connected number is an E.164 number, it is set as“TEL URL” in a Request-URI header of the SIP OPTIONS message. PS core100C then translates the received TEL URL into a valid SIP URI (UnifiedResource Identifier) by means of well-known IETF standards.

In the case if unit B2 is a voice mail apparatus having theabove-mentioned exemplary number 888-0709123456, PS core 100C wouldtranslate it into, e.g., 0709123456@voicemail45.teliasonera.net, where avoice mail system #45 in a Telia-Sonera network may be designated tohandle all 0709-numbers. The receiving voice mail apparatus would thenbe able to identify the called subscriber by reading the number fieldprior to the symbol “@”.

PS core 100C then conveys the capability query, including the translatednumber of B2 (e.g. a valid SIP URI), to PS core 104C in a next step 326.Thereafter, the capability query is sent in a step 328 to the secondaryunit B2, using the IP address of unit B2 in that network as thedestination address, as derived from the connected number translated instep 324. Unit B2 then duly sends a response including the requestedcapabilities towards the calling terminal A, in a step 330, which inpractice is conveyed by means of the intermediate PS cores 104C and100C, although not specifically shown here. In the IMS context, thisresponse would be a conventional message called “SIP 200 OK/SDP”.

After receiving the requested capabilities, terminal A can determinewhich multimedia options are available with respect to the mutualcapabilities of A and B2, and display them on its screen, in a step 332.The user of terminal A is then free to select from the displayedmultimedia options and initiate a session with unit B2. Moreover, theopposite unit B2 may likewise display the same available multimediaoptions on its screen, as indicated in a step 334, since thecapabilities of terminal A were typically included in the query conveyedin steps 322-328. Thereafter, either of terminal A and unit B2 mayinitiate a session starting with a session invitation message asindicated in a step 336, e.g. SIP INVITE. A conventional sessionprocedure will then be executed as indicated in a final step 338, notdescribed here further.

Hence, the present solution includes obtaining the connected number,preferably regardless of whether a COLP service or the equivalent isused or not, storing the connected number, and requesting capabilitiesfrom the correct terminal currently in connection, based on the storedconnected number. Alternatively, the capabilities of unit B2 may havebeen cached at terminal A in connection with a previous multimediasession, e.g. as disclosed in PCT/SE03/01901. In that case, the cachedcapabilities are stored together with a key or the like, which ispreferably the telephone number of the corresponding terminal. Thecached capabilities can therefore be retrieved if the stored connectednumber matches that key, and no capability exchange would then benecessary to perform.

FIG. 4 is a flow chart illustrating an exemplary procedure, according toanother embodiment, of determining available multimedia options duringan ongoing circuit-switched call, in particular with respect tocall-forwarding. This procedure is basically executed by the callingterminal and will now be described again with further reference to thescenario in FIG. 1.

In a first step 400, terminal A directs an ordinary circuit-switchedvoice call to a primary unit B1, just as in step 200 of FIG. 2. The nextstep 402 of detecting whether a connected number has been receivedduring a call set-up procedure, basically corresponds to step 202 ofFIG. 2. If not, the capabilities of the called unit B1 may be determinedbased on the called number as in any conventional procedure, in afollowing step 404.

However, if it is detected in step 402 that a connected number has infact been received, the following steps 406-414 are taken in order todetermine the capabilities of the connected unit, such that theavailable multimedia options can be determined and a multimedia sessioncan be conducted, if desired. It should be noted that this procedure canbe used regardless of whether the call has been forwarded to a secondaryunit B2 or not. That is, the calling terminal needs not detect anycall-forwarding state. The capability determination is preferablyexecuted automatically after the call has been set up, but mayalternatively be executed in response to some input from the userindicating that capabilities must be determined, such as a multimediaapplication activation or a multimedia options query.

First in a step 406, terminal A stores the received connected number.The received number may either be that of the called primary unit B1 ifno call-forwarding, or that of a secondary unit B2 to which the call hasbeen forwarded, e.g. as obtained in the procedure of steps 308-316 inFIG. 3. In a step 408, it is checked whether the capabilities of theassociated unit, either B1 or B2, have been cached in terminal A, usingthe stored connected number as described above. If so, the cachedcapabilities are retrieved by using the connected number as a key in astep 410, and if not, a capability exchange procedure is executed basedon the stored connected number, in a step 412, e.g. as in the procedureof steps 322-330 in FIG. 3. Thus, the stored connected number is used asthe destination address for either a capability query (e.g. SIP OPTIONS)or a session invitation (e.g. SIP INVITE).

After the capabilities of the other communication unit in the call havebeen determined, i.e. as in any of steps 404, 410 or 412, the availablemultimedia options can be finally determined in a step 414. Thereafter,the available multimedia options may be displayed to the user on theterminal screen and a multimedia session may be started, as indicated ina final optional step 416.

Finally, it should be noted that the connected number of a secondarycommunication unit to which an ongoing call is forwarded can be obtainedby the calling terminal according to different mechanisms. In oneembodiment, the connected number may be automatically provided from theCS core (e.g. 104 c) of the secondary unit, e.g. by means of a COLPservice or the like. In other embodiments, the connected number may beactually requested either by the calling terminal (e.g. A), by the CScore (e.g. 100 c) of the calling terminal, or by the CS core (e.g. 102c) of the originally called terminal. However, in existing systems oftoday a COLP subscription is in fact necessary to ensure that thecalling terminal will obtain a connected number during the call set-up.

While the invention has been described with reference to specificexemplary embodiments, the description is generally only intended toillustrate the inventive concept and should not be taken as limiting thescope of the invention. For example, the described “secondary unit”could be a communication terminal or a voice mail apparatus or theequivalent. The present invention is generally defined by the appendedclaims.

The invention claimed is:
 1. A method of enabling communication ofInternet Protocol (IP) multimedia content to a called user, comprising:directing a call from a calling terminal to a primary communicationunit, wherein the primary communication unit is a communication terminalhaving a called number associated therewith; receiving by the callingterminal a connected number during a call set-up procedure when the callhas been forwarded by the primary communication unit to a secondarycommunication unit, wherein the connected number is associated with thesecondary communication unit; storing the received connected number; anddetermining multimedia capabilities of the secondary communication unitbased on the connected number.
 2. The method according to claim 1,further comprising the step of determining available multimedia optionsbased on the determined multimedia capabilities of the secondarycommunication unit.
 3. The method according to claim 1, wherein theconnected number is received as the calling terminal subscribes to aconnected line presentation (COLP) service.
 4. The method according toclaim 1, wherein the secondary communication unit is a communicationterminal or a voice mail apparatus.
 5. The method according to claim 1,wherein the multimedia capabilities of the secondary communication unitare determined by requesting capabilities from the secondarycommunication unit based on the stored connected number.
 6. The methodaccording to claim 5, wherein capabilities are requested from thesecondary communication unit by sending a capability query or a sessioninvitation using the stored connected number as a destination address.7. The method according to claim 1, wherein the multimedia capabilitiesof the secondary communication unit are determined by retrieving cachedcapabilities of the secondary unit based on the stored connected number.8. The method according to claim 7, wherein the cached capabilities areretrieved by using the connected number as a key.
 9. A communicationterminal capable of Internet Protocol (IP) multimedia communication,comprising: means for directing a call from the communication terminalto a primary communication unit, wherein the primary communication unitis a communication terminal having a called number associated therewith;means for receiving by the communication terminal a connected numberduring a call set up procedure when the call has been forwarded to asecondary communication unit, wherein the connected number is associatedwith the secondary communication unit; means for storing the receivedconnected number; and means for determining multimedia capabilities ofthe secondary communication unit based on the connected number.
 10. Thecommunication terminal according to claim 9, wherein the terminal isadapted to determine available multimedia options based on thedetermined multimedia capabilities of the secondary communication unit.11. The communication terminal according to claim 9, wherein theterminal is adapted to receive the connected number by means ofsubscription to a connected line presentation (COLP) service.
 12. Thecommunication terminal according to claim 9, wherein the terminal isadapted to determine the multimedia capabilities of the secondarycommunication unit by requesting capabilities from the secondarycommunication unit based on the stored connected number.
 13. Thecommunication terminal according to claim 12, wherein the terminal isfurther adapted to request capabilities from the secondary communicationunit by sending a capability query or a session invitation using thestored connected number as a destination address.
 14. The communicationterminal according to claim 9, wherein the terminal is adapted todetermine the multimedia capabilities of the secondary communicationunit by retrieving cached capabilities of the secondary communicationunit based on the stored connected number.
 15. The communicationterminal according to claim 14, wherein the terminal is further adaptedto retrieve the cached capabilities by using the connected number as akey.